Solid state lithium-iodine primary battery

ABSTRACT

A substantially anhydrous solid state battery has a lithium anode, a solid lithium iodide electrolyte and an electronically conductive cathode containing iodine, such as organic iodine charge transfer complexes.

United States Patent Moser [451 May 2,1972

[72] Inventor:

[73] Assignee: Catalyst Research Corporation, Baltimore,

[22] Filed: June 1,1970

[21] AppLNo; 41,801

James R. Moser, Shrewsbury, Pa.

[52] US. C1. ..136/83 R, 136/137 [51] 1nt.C1. ..110lm 21/00 [58] FieldofSearch ..136/83, 153,137,111, 86, 136/6, 136

[56] References Cited UNITED STATES PATENTS 3,455,742 7/1969 Rao..136/83 3,438,813 4/1969 Davis ..136/83 Wilson et a1 136/1 37 3,057,76010/1962 Dereska et a1. 1 36/ l 37 3,235,408 2/1966 Harris 136/1 37 X2,953,620 9/1960 Smyth et a1... ..136/83 3,073,884 1/1963 Pinkerton..136/l00 3,443,997 5/1969 Argue et al. 1 36/1 53 X 3,463,670 8/1969 Raoet al 136/83 2,954,417 9/1960 Lehovec et al ..136/153 X 3,498,843 3/1970Hunt et al ..136/83 Primary Examiner-Anthony Skapars Attorney-Ronald H.Shakely [5 7] ABSTRACT A substantially anhydrous solid state battery hasa lithium anode, a'solid lithium iodide electrolyte and anelectronically conductive cathode containing iodine, such as organiciodine charge transfer complexes.

21 Claims, 3 Drawing Figures INVENTOR JAMES R. MOSER FIG. I

SOLID STATE LITHIUM-IODINE PRIMARY BATTERY This invention relates to asolid state primary cell having a lithium anode, an iodine cathode and asolid lithium halide electrolyte.

Gutman et al, J. Electrochem. Soc., 114, 323 (1967) made solid statecells utilizing anodes of certain divalent metals or silver and cathodesof electronically conducting charge transfer complexes; report energydensities of l watt-hour per pound and flash currents of 25 ma/cm fromcells with a magnesium anode and organic-iodine cathode. The sameauthors, J. Electrochem. Soc., 115, 359 (1968), report significantincrease in flash current on admission of vapors of high permittivityliquids, such as'water, to the anode-electrolyte interface.

It is an object of this invention to provide a solid state highvoltage,high energy density battery especially useful for long life, low currentdrain applications. The lithium-iodine cells of this invention have ahighoutput voltage, typically an open circuit voltage of 2.7 to 3.0volts depending primarily on cell design and the cathode material. Thesystem has a theoretical energy density of about 213 watt-hours perpound and energy densities as high as 136 watt-hours per pound have beenobtained during discharge of encapsulated cells at room temperature.

The cells of this invention comprise a'lithium anode, a solid statelithium halide electrolyte, and a solid state electronically conductivecathode that contains iodine. The anode reaction Y Li Li e and thecathode reaction is I, +2e 2I giving an overall reaction 2Li +1 2LiI.

This electrochemical system is especially advantageous in that lithiumhas a high energy density, as the most electropositive'metal with thelowest equivalent weight, and the electrolyte formed on discharge of thecell is Lil, the lithium salt having the highest ionic conductivity,much higher than the ionic conductivity of divalent halides.

The cathode iodine may be free iodine intimately admixed with a solidelectronic conductor or, preferably, it is at least partially chemicallybound as in organic-iodine charge transfer complexes. The electrolyte ispreferably lithium iodide, which may be formed in situ by contacting theanode and cathode surfaces, whereby lithium reacts with iodine in thecathode to form a solid lithium iodide electrolyte layer contacting theanode and cathode. Alternatively, the electrolyte includes a coating oflithium iodide or other lithium halide on the lithium anode formed byreaction of the lithium with iodine or another halogen. The cathode isgenerally contacted against an inert current collector, suitably carbonor a metal inert to the cathode. An inert metal current collector isalso generally used as a convenient method of providing electricalconnection to the soft lithium anode.

In the accompanying drawings, FIG. I is an exploded perspective viewshowing the components of a cell in accordance with this invention;

' FIG. 2 shows the assembled cell of FIG. 1 encapsulated in a pottingcompound; and

FIG. 3 is a sectional view of a preferred thin cell made in accordancewith this invention.

Referring to FIG. 1, the cell comprises a metal anode contact member orcurrent collector 2, a sheet lithium anode 4, a cathode 6, and a cathodecurrent collector consisting of a metal screen 8 that is preferablyspot-welded to a metal sheet 10. The cell components are stacked and thestack is compressed suitably at pressure of about 1000 psig., to form acomplete cell. The anode contact member has holes 12 punched by a nailorother conical punch, giving projecting sharp edges that dig into andsecure the contact member to the lithium anode. A metal screen or gauzemay also be used to advantage as an anode contact member. The cathodematerial, suitably finely divided, is'compacted when forming the cellinto a solid disc having embedded therein the cathode contact screen 8.lfdesired, the cathode material may be compacted into a pellet of thedesired size prior to assembly into the cell.

As shown in FIG. 2, the resulting cell, which has a plurality oflaminated layers in intimate contact, is then encapsulated in an inertpotting compound 14, suitably a polyester, that serves to protect thecell from degradation or exposure to the atmosphere.

A lithium iodide electrolyte is formed in situ by reaction of the iodinein the cathode with the lithium anode. It is equally satisfactory, andin some instances preferable, to fonn a film of lithium salt electrolyteon the anode surface abutting the cathode prior to cell assembly, mostconveniently by exposing the anode surface to dry air or argonatmosphere containing halogen gas or vapor. It will be recognized thatadditional lithium iodide electrolyte is formed by the electrochemicalreaction of the cell.

The cell of FIG. 3 may be made in the form of a thin sheet, as little as15 to 20 mils thick, of any size. The cell is enclosed in plasticenvelope I6, suitably polyvinyl chloride, such as Process 40, Teflon orother plastic film impervious to iodine and ordinary atmospheres, thatis, oxygen, nitrogen and water vapor. A thin metallic anode currentcollector l8, suitably a nickel plate deposited on the plastic envelopeby vacuum deposition or electroless plating, abuts a thin lithiumelectrode 19, suitably l to 10 mils thick. The lithium is mostconveniently in the form of a foil,'but it may also be deposited on thecurrent collector by vacuum deposition, electroplating or otherconventional methods. The initial thin film of lithium iodideelectrolyte 20, may, as previously described, be preformed on thelithium surface before assembling the cell or formed spontaneously whenthe clean lithium anode surface is brought into contact with thecathode. The cathode 22 may be a compacted powder or is moreconveniently applied to the anode as a paste of cathode material orcathode material and binder, for example, vinyl dispersions such asOKuns Liquid Vinyl. The cathode current collector 24 may be a thin metalfoil or, as in the case of the anode current collector, a metal coatingdeposited on the plastic envelope. Metal leads 26 and 28, for externalcircuit connections, are connected to the anode and cathode currentcollectors respectively and tightly sealed through openings in theplastic envelope.

The cells of this invention are adversely affected by atmosphericmoisture, so cells are assembled and encapsulated in a dry atmosphere,suitably in dry rooms or enclosures hav ing a relative humidity lessthan about 2 percent, using substantially anhydrous and/or driedcomponents. All of the cell assemblies and tests of non-encapsulatedcells described herein were performed in such a dry room or in dry boxeshaving even dried air or argon atmospheres.

Charge transfer complexes of an organic material and iodine arepreferred cathode materials for use in this invention, although anyother cathode may be used that is electronically conductive and containsavailable iodine for the electrochemical reaction. Charge transfercomplexes are a wellknown class of materials that have two components,one an electron donor, the other an electron acceptor, that form Weaklybonded complexes that exhibit electronic conductivity higher than eithercomponent. Suitable charge transfer complexes for this invention consistof an organic donor component and iodine, the electron acceptor,preferably having a conductivity of greater than about 2.5 X 10'4mho/cm. The charge transfer complexes are in chemical equilibrium withsome small amount of free iodine that is available for electrochemicalreaction. These charge transfer complexes have a wide range ofelectronic conductivity, and if the conductivity is low, the currentoutput will be comparatively low because of the high internal ohmicresistance. Cathodes containing intimate mixtures of such lowconductivity complexes with powdered graphite or inert metal have highconductivities and can provide performance comparable to cells usinghigh conduc' tivity complexes. Suitable charge transfer complexes may beprepared using as organic donor components polycylic aromatic compounds,such as, for example, pyrene, perylene,

anthracene, naphthalene erythrosine, azulene and fluorene; organicpolymers, such as, for example, polyethylene, polypropylene,polystyrene, polypyrrole, polyamides and polyvinyls; or heterocycliccompounds,-containing nitrogen or sulfur, such as, for example,phenothiazine, phenazine, lphenylphenophiozine, thianthrene,lO-methylthiazine and methalyineblue; and polymerized or polymerizablecompounds in which a heterocyclic nitrogen moiety is incorporated as aside chain or substituent, especially vinyl compounds and polymers, suchas poly-2-vinyl quinoline, poly-2- vinyl pyridine, poly-4-vinylpyridine, poly--vinyl-2-methylpyridine and poly-N-vinyl carbazole. Theproportions of iodine toorganic component can be varied over a widerange, although a high proportici of uncomplexed iodine in the organicmaterials used were those that react spontaneously with iodine to form acharge transfer complex. In some cases,

cleaned with petroleum ether and scraped. The cell was tested for opencircuit voltage (O.C.V.), current output at various voltages (pA/V), andshort circuit current (S.C.C.' The cells were then coated with lacquerand retested in 24 hours. Typical results are shown in Table I.

TABLE 1 Initial test 24 hour test Battery number Cathode compositionO.C.V S.C.C. A) A/V A/V O.C.V. 8.0.0. A) A/V l. 00% iodine, 1% carbon 1.61 24 0. 6/1. 54 24/0. 04 O. 40 21 Q0/0113 .2 05?} 10111119, 5% carbon2.85 4, 600 1. 05/2. 85 1, 470/2. 35 2.80 680 470/0. 75 3 00% iodine,10% carbon 2.00 6, 300 1. 10/2. 00 1, 530/2. 50 2. 85 '1, 100 760/1. 254 50% iodine, 50% polyethylene. 2.90 122 1. 05/2. 75 110/0. 20 2.80 1,450 120/1. 5 50% iodine, 50% polypropylene 2. 90 145 1. 00/2. 80 130/0.2. 85 710 500/0. 50

6 47%7 lOdlll0,-1T /g% polypropylene, 5%

carbon 2. 85 470 1. 00/2. 85 380/0. 65 z. 75 1, 650 790/1. Pyiene 2 12 12. 05 630 1. 10/2. 05 450/0. 80 2. 95 150 135/0. 30 50% pyrene 2 12 l50% iodine. 3.00 480 1. 10/3. 00 370/0. 70 2. 00 305 255/0. -15 Pyi'ene2 I2 2 3.00 1, 600 1.10/3.00 770/1. 2.05 3,100 1050/1. 85 50% pyrene-2I: 2 50% iodine- 3.00 2, 000 1. 10/3. 00 860/1. 45 Z. 85 l, 100 600/1.00 50% iodine, 50% plienothiazii 2. 95 1, 200 1. 07/2. 95 680/1. 15 2 001, 450 740/1. 25

12 47%72, iodine 47%% phenothi carbon. 2. 00 2, 700 1. 02/2. 00 1,050/1. 85 2 85 1, 750 820/1. 35 13... 2 phenothlazlne 3 I 2. 85 118 1.07/2. 85 104/0. 20 2. 85 102 93/0. l5 l4 Perylene I; 2.01 2,700 2. 803,700

' Prepared by melting together pyrene and iodine.

2 Prepared by prec pitation from 001 solution. 3 Prepared byprecipitation from benzene solution.

densities, on the order of 50 to 100 ,uA/cm the voltage decay of my newcells is linear with time. Generally, curves of cell voltage againsttime for discharge at such high current densities follow the equation-:

1; =C-(i/A 't' exp(8650/RT) where 1; is polarization, [IA is the currentdensity and C is a constant. dependent on cell preparation, methods andcathode material, typically C equals about 1.25 X l0-4(ohm-cmV/coulombs. There is markedly less polarization when cells aredischarged at smaller current densities, for example, l0-25 ,uA/cm? Atlower current densities, allowing cells to run for longer times,deviations from linearity are evident in discharge .curves, especiallyat higher temperatures, which are the result of self-discharge.

Self-discharge involves diffusion of iodine from the cathode through theLil electrolyte to the anode where additional electrolyte is thengenerated. This internal cell resistance resulting from the accumulationof electrolyte is dependent on the square root of storage time, as istypical for diffusion limited reactions. Although after long storageperiods, the increase of internal resistance permits drawing only smallcurrents, on the order of l nA/cm", such currents can be sustained forlong periods of time.

The cells of this invention are more fully described in relation to thefollowing illustrative examples:

EXAMPLE I Primary cells were made using various electronicallyconductive cathodes containing iodine available for electrochemicalreaction. Cathodes were made by mixingiodine with the other powderedcathode components, graphite and/or an organic material, and the mixturewas compacted at 5250 psig. into a pellet 1.25 cm. in diameter and about1 mm. thick. The

Other organic materials used with iodine in cells with similarperformance, either with or without 5 to 10 percent added graphite,include nylon, Lucite, Lucite paste in dichloroethylene, pyrrole,polypyrrole, naphthalene, dimethyl glyoxime, phenolphthalien,phthalimide, erythrosine, methylene blue, urea, brominated pyrene,Teflon and otolidine.

EXAMPLE 11 lithium anode before assembly of the cell to diminishinternal I short circuiting. The electrolyte film is formed by exposingthe lithium surface to a dry air or argon atmosphere containing a vaporreactive with lithium to form a conductive salt of lithium, preferablythe halogens, 1 C1,, or Br although other reactive vapors may be used,such as methanol or ethyl ether. To illustrate, cells were made inaccordance with Example 1 having a cathode of 47% percent pyrene'2I 47%percent iodine and 5 percent powdered carbon; one cell had a cleanlithium anode and a second cell had a lithium anode coated with an Lilfilm. The results from performance tests as in Ex- Six cells one-halfinch in diameter and 0.215 inch thick were made in accordance with FIG.1 in which the anode contact was nickel foil, the anode was lithium, thecathode contact was 60 mesh nickel gauze and the cathode was a pellet of2 phenothiazine-3I charge transfer complex prepared by mixing togetherand heating phenothiazine and iodine in the indicated proportions. Thelithium anode surface abutting the cathode was coated with a film of Lilformed by exposing the surface to iodine vapor in an argon atmosphere.The cell components were stacked and compressed at 1100 psig. to formthe completed cell assembly. The cells were continuously discharged at acurrent of 25uA at 33C. Table 3 shows the voltage at 25,u.A currentdrains and the short circuit current at complex containing 105 parts byweight poly-4-vinyl pyridine to 254 parts of iodine. The precipitate wasfiltered, vacuum dired and 3 parts of the complex were mixed with partsof powdered iodine. This mixture was pressed into inch diameter discs at50 psig. for use as cathodes. Cells as shown in FIG. 1 were made usingthe cathode material, a lithium anode cut from H 16-inch thick anode andcathode collectors; the cell being compressed at 10 psig. and potted inpolyester potting compound. The performance characteristics of cellswere various time intervals. 10 measured as f ll s;

TABLE 3 O.C.V. 2.9 V S.C.C. 2.5 ma Life at Room Temperature discharge atTime volts at I-"* SCC (I SOuA/cni current density 333 hours Life atRoom Temperature discharge at 0 2 (5-2 7 100pA/cm current density 141hours 1 Cell voltage after 645 hours discharge Room Temperature at10;;A/cm 60C at l0pA/cm 2 3s v 00-1600 2 3 2.4 250400 -40C. at0.2;1.A/cm 0.60 V. 49 1.3-1.5 50-80 Another cell, identical except that5-vinyl-2-methylpyridine was used in place of 4-vinylpyridine had a celllife of 250 hours EXAMPLE W 25 at a discharge rate of 50,u.A/cm at roomtemperature. Cells were made as in Example 111, except that chargetransfer complex contained different proportions of iodine. EXAMPLE VIIThe cells were continuously discharged at a current of 25,1.A andperiodic measurements were made of open circuit voltage It has beenjointly discovered with Alan A. Schneider, of and 0f the c r nt outputat a l ge n -h the open CiICUiI 30 Baltimore, Maryland, that cells inaccordance with this inveng as Set out in Table tion and having cathodesof poly-2-vinylpyridine-iodine or TABLE 4 O. O. V. (volts) CurrentOutput at 0. C.V. (MA) (nthodo 0 hrs. 16 hrs. 46 hrs. 52 hrs. 63 hrs. 0hr 16 lllS. 46 hrs. 52 hrs. 63 hrs 2 phonothinzino '2 1;. 2. 7 2. 7 2. 01,500 8 2 plu'nothinzino 3 I 2. 7 2. 8 2. 9 2. 9 2,100 5 2 phonothiuzino4 1g. 2.8 2. 9 2. 9 2. 9 3,100 4. 8 2 phonothiazinc 4% 1L 2. U 2. 9 2. 9550 4- 8 The performance of cells containing or using 2Phenothiazine-cOl or larger proportions of iodine becomes comparable ondischarge of the cell, although the initial per formance cells with moreiodine than about 2 Phen0thiazine-4 l, is diminished because of thehigher ohmic resistance of such cathodes. When using less iodine thanabout 2 Phenothiazine-2D2, the performance over the entire lifedecreased apparently due to less available iodine.

EXAMPLE Cells were made in which 2 Phenothiazine'3l complex was mixedwith a binder and painted on a nickel collector and contacted against alithium foil disc anode to form a complete cell one-half inch indiameter. The cells were discharged to zero voltage at a current densityof 50,u.A/cm giving the life shown in Table 5 for varying proportions ofbinder and charge transfer complex.

Poly-4-vinyl pyridine'I (P4VP'l complex was prepared by polymerizing4-vinyl pyridine in benezene solution using n-butyllithiumpolymerization initiator, and then adding an excess of iodine solutionin benzene to precipitate the charge transferpoly-2-vinylquinoline-iodine charge transfer complexes with excess ofiodine exhibit unexpected superior performance several times better eventhan other cells of this invention. Poly-2-vinylpyridine'l orpoly-2-vinylquinoline-l charge transfer complexes are prepared inbenzene as in Example V1 except using either 2-vinylpyridine or2-vinylquinoline in place of the 4-viny1pyridine. The complexesprecipitated from the benzene contain a stoichiometric amount of iodine,that is 71 percent 1 in the case of poly-2-vinylpyridine and 62 percent1 in the case of poly-Z-vinylquinoline. When either of these chargecomplexes are mixed with about 3 to 15 parts of iodine for each part ofcomplex, a paste-like solid is formed that is sufficiently plastic to beeasily spread on a solid substrate, such as the lithium anode or a metalcurrent collector. It is believed that the plastic state of thematerials permit excellent atomic bonding of the cathode to the anodeand to the cathode current collector resulting in greater outputs fromthe cell. In addition, this material has substantially the sameelectrical resistance over a wide range of iodine content, so that thecathode resistance does not change during cell discharge. The preferredcathode contains from about 10 to 15 parts 1 to each part chargetransfer complex.

To illustrate the much superior performance of such cells, Cells made asillustrated in FIG. 3, with a 0.012 inch thick lithium anode and a 0.048inch thick cathode of 10 parts 1 for each part poly-2-vinylpyridine'l(93.2 percent by weight iodine, 6.8 percent by weightpoly-2-vinylpyridine) had open circuit voltage of 2.80 volts and a cellvoltage of 0.24 volts after 1000 hours discharge at a current density ofSOuA/cm; 2.16 volts after 1000 hours discharge at 25uA/cm and 2.69 voltsafter 1000 hours discharge at lOuA/cm.

I claim:

l. A substantially anhydrous cell comprising a solid lithium anode, asolid lithium iodide electrolyte and a solid electronically conductiveiodine cathode containing a charge transfer complex of an organic donorcomponent and iodine.

2. A cell according to claim 1 in which the cathode contains carbon.

3. A cell according to claim 1 in which the organic component is aheterocyclic nitrogen compound.

4. A cell according to claim 3 in which the heterocyclic compound isphenothiazine.

5. A cell according to claim 3 in which the heterocyclic compound is apolymer of a vinyl compound having a heterocyclic nitrogen substituent.

6. A cell according to claim 5 in which the heterocyclic compound ispoly-4-vinylpyridine.

7. A cell according to claim 1 in which the organic donor component is apolycyclic aromatic compound.

8. A cell according to claim 1 in which the cathode consists of amixture iodine and the charge transfer complex.

9. A cell according to claim 8 in which the organic component is aheterocyclic nitrogen compound.

10. A cell according to claim 9 in which the organic component isphenothiazine.

11. A cell according to claim 9 in which the organic component ispoly-4-vinylpyridine.

12. A cell according to claim 10 in which the proportion ofphenothiazine to iodine is between about 3 to l and 4 to l.

13. A cell according to claim 1 in which the anode surface is coatedwith a lithium halide.

14. A cell according to claim 13 in which the halide is lithium iodide.

15. A primary cell according to claim 1 comprising a laminate of theanode and cathode, the electronically conductive component of saidcathode consisting of a charge transfer complex of an organic donorcomponent and iodine, said anode and cathode forming therebetween asolid Lil laminae.

16. A cell according to claim 15 in which the cathode is a mixture ofiodine and charge transfer complex.

17. A cell according to claim 16 in which the organic component is aheterocyclic nitrogen compound.

18. A cell according to claim 17 in which the organic component is apolymer of a vinyl compound having a heterocyclic nitrogen substituent.

19. A cell according to claim 15 enclosed in a flexible plastic filmsubstantially impervious to iodine, oxygen, nitrogen and water vapor.

20. A cell according to claim 1 encapsulated in a material substantiallyimpervious to iodine, oxygen, nitrogen and water vapor.

21. A cell according to claim 18 in which the heterocyclic component ispoly-4-vinylpyridine.

2. A cell according to claim 1 in which the cathode contains carbon. 3.A cell according to claim 1 in which the organic component is aheterocyclic nitrogen compound.
 4. A cell according to claim 3 in whichthe heterocyclic compound is phenothiazine.
 5. A cell according to claim3 in which the heterocyclic compound is a polymer of a vinyl compoundhaving a heterocyclic nitrogen substituent.
 6. A cell according to claim5 in which the heterocyclic compound is poly-4-vinylpyridine.
 7. A cellaccording to claim 1 in which the organic donor component is apolycyclic aromatic compound.
 8. A cell according to claim 1 in whichthe cathode consists of a mixture iodine and the charge transfercomplex.
 9. A cell according to claim 8 in which the organic componentis a heterocyclic nitrogen compound.
 10. A cell according to claim 9 inwhich the organic component is phenothiazine.
 11. A cell according toclaim 9 in which the organic component is poly-4-vinylpyridine.
 12. Acell according to claim 10 in which the proportion of phenothiazine toiodine is between about 3 to 1 and 4 to
 1. 13. A cell according to claim1 in which the anode surface is coated with a lithium halide.
 14. A cellaccording to claim 13 in which the halide is lithium iodide.
 15. Aprimary cell according to claim 1 comprising a laminate of the anode andcathode, the electronically conductive component of said cathodeconsisting of a charge transfer complex of an organic donor componentand iodine, said anode and cathode forming therebetween a solid LiIlaminae.
 16. A cell according to claim 15 in which the cathode is amixture of iodine and charge transfer complex.
 17. A cell according toclaim 16 in which the organic component is a heterocyclic nitrogencompound.
 18. A cell according to claim 17 in which the organiccomponent is a polymer of a vinyl compounD having a heterocyclicnitrogen substituent.
 19. A cell according to claim 15 enclosed in aflexible plastic film substantially impervious to iodine, oxygen,nitrogen and water vapor.
 20. A cell according to claim 1 encapsulatedin a material substantially impervious to iodine, oxygen, nitrogen andwater vapor.
 21. A cell according to claim 18 in which the heterocycliccomponent is poly-4-vinylpyridine.